1. Field of the Invention
The present invention relates to a communications terminal unit to be connected to an Internet protocol (IP) network and a public switched telephone network, and to a method for controlling the unit. More specifically, the invention relates to a communications terminal unit having the function of automatically determining whether to originate a call over an IP network or over a public switched telephone network by analyzing a communication error in the event that the communication error has arisen when a call is originated by selection of an IP network or the public switched telephone network, as well as to a method for controlling the unit.
2. Description of the Related Art
For example, some facsimile machines are connected to both an IP network and a public switched telephone network. In the case of a related-art facsimile machine of this type, a user selects “FAX” in which a call is originated over the public switched telephone network, or “iFAX” in which a call is originated over the IP network.
However, in the case of the facsimile machine which originates a call in accordance with the user's selection of a network, an indispensable feature is for all users to be able to ascertain whether or not a call can be originated to a call receiver over the IP network, or whether or not origination of a call over the public switched telephone network incurs a low communication cost.
If this is ignored, there may arise, for example, a case where a waste of communication cost occurs when a call is originated over the public switched telephone network despite the possibility of originating a call over the IP network.
In contrast, when, in spite of the impossibility of originating a call over the IP network, an attempt is made to originate a call over the IP network, a communication error arises.
In this case, the related-art facsimile machine repeats origination of a call over the same network only a predetermined number of times at predetermined re-dialing intervals. In contrast to a case where the party on the other end of the line is busy, communication cannot be established permanently, because a call is originated to a network to which a call cannot essentially be originated.
As mentioned above, in the case of the related-art facsimile machine connected to both the IP network and the public switched telephone network, the user selects one from the IP network and the public switched telephone network, thereby originating a call. However, if an inappropriate network is selected, a call will be originated over, e.g., a network to which a call cannot be originated, thereby inducing a communication error. Thus, the related-art facsimile machine presents a problem of low reliability of information transmission.